The present invention relates to an electromagnetic delay line, and in particular to an improvement of such an electromagnetic delay line having an electroconductive zigzag strip disposed to face a ground electrode with a dielectric layer therebetween.
This type of an electromagnetic delay line (shown in FIG. 4) heretofore known has a structure configured by having a ground electrode 3 formed on one face (lower face in the drawing) of a dielectric layer 1 and serially connecting each of a plurality of main electroconductive strips 5 arranged in parallel at certain intervals in the longitudinal direction of this dielectric layer 1 on the other side (upper face in the drawing) of the dielectric layer 1, thereby forming a zigzag strip 7.
In FIG. 4, reference numeral 9 is a secondary electroconductive strip to connect in series the neighboring main electroconductive strips 5 to form the zigzag strip 7.
This type of an electromagnetic delay line, applying a pulse signal to the zigzag strip 7 with its one end as an input terminal, outputs the pulse signal from the other end of the zigzag strip 7 accompanying a delay time corresponding to the length of the zigzag strip 7.
Therefore, the delay time can be increased by enlarging the length of the main electroconductive strips 5 or the width W and a size in the longitudinal direction L crossing at a right angel with the width W of the zigzag strip 7.
The delay time can be also increased with an area occupied by the electromagnetic delay line unchanged by making the main electroconductive strip 5 thinner and approaching the neighboring main electroconductive strips 5 to each other to increase the number of the main electroconductive strips 5.
In the above configured electromagnetic delay line, however, as shown in FIG. 5 illustrating a sectional view taken in a plane shown by the arrows V--V in FIG. 4, the neighboring main electroconductive strips 5 have the signal flown in opposite direction, every other main electroconductive strips 5 have the signal flown in the same direction, and every two other main electroconductive strips 5 have the signal flown in opposite direction. So, positive and negative couplings are generated alternately between the neighboring main electroconductive strips 5 when seen based on any main electroconductive strip 5.
Therefore, coupling coefficients between two immediately neighboring main electroconductive strips 5 and between every two other main electroconductive strips 5 have negative values (-k1, -k3), while it has a positive value (k2) between the two main electroconductive strips 5 with another main electroconductive strip 5 therebetween.
Specifically, the negative value (-k1) between the mainly neighboring main electroconductive strips 5 comes to have a large value, giving a great influence to the delay characteristics.
Consequently, the above electromagnetic delay line has drawbacks that the negative coupling coefficient of the zigzag strip 7 tends to be great, resulting in making an output waveform have a high overshoot A as shown in FIG. 6.
Particularly, the overshoot becomes particularly great to degrade the delay characteristics when the width W is increased in the zigzag strip 7 or when main electroconductive strips 5 are made thinner and positioned to be close to increase a delay time.